The central goal of this project is to develop the potential of the recently made observation that there are antibody responses to thymic antigens specific for the dermatomyositis (DM) and polymyositis (PM) syndromes. In the initial reports, these serological reactions utilized crude extracts of thymus tissue as antigen. Sixty percent of all patients with these diseases possess precipitating antibodies to these antigens. Recent studies with the indirect immunofluorescent technique utilizing human tissue culture lines reveal that at least 80 percent of the patients without precepitins have antibodies. Thus more than 90 percent of all patients with PM and DM have demonstrable humoral autoimmune responses. Purification of these antigens would permit the collection of several types of data which are of clinical, immunological, and biological interest. Clear resolution of the apparent heterogeneity of these reactions with purified antigens will make possible the quantitative assessment of humoral and cellular immune responses in patients. Knowledge of the existence of this humoral and cellular immunity will also permit an assessment of whether there are correlations between these immunological responses and disease activity, the presence or absence of tumor, or prognosis.